1. Field of the Invention
The present invention relates to a method of treating a semiconductor substrate with fluid (especially with liquid) and an apparatus for the same and, more particularly, to a method of treating only one surface of a flat substrate for use in a semiconductor device or a liquid crystal display device and an apparatus for the same.
2. Description of the Related Art
As steps of treating a semiconductor substrate (silicon wafer) with chemicals, there are various steps such as photoresist applying, etching, cleaning, photoresist removing, developing, plating, etc. A conventional steps of treating a silicon wafer with chemicals will be described in detail.
FIG. 1 is a crosssectional view of a treatment apparatus wherein a silicon wafer is immersed in a treatment tub 11 to be treated. In case of wafer cleaning or resist removing, a treatment liquid 12 is composed of H.sub.2 SO.sub.4 and H.sub.2 O.sub.2 mixed in a ratio of 10:1, for example, and is filled in a treatment tub 11 by a total amount of 25 l. The treatment tub 11 is made of quartz or the like. The treatment liquid 12 is heated by a lamp heater 13 to about 150.degree. C. A plurality of, for example, 25 sheets of silicon wafers 14, i.e, substrates to be treated, on which resist patterns each of a diameter of 150 mm, for example, are formed are held in a wafer holder 15 and they are immersed in the treatment liquid 12. The cleaning step and the resist removing step are completed by immersing the wafers 14 in the treatment liquid 12 for about 15 minutes. About 500 sheets of wafers 14 can be treated with the treatment liquid 12 of 25 l.
In an etching step of a glass layer, an ammonium fluoride (NH.sub.4 F) or a diluted hydrofluoric acid (HF) is used as the treatment liquid 12. In an etching step of a silicon layer, a solution of organic alkali is used as the treatment liquid 12. In order to remove an oxide film formed on the rear surface of the silicon wafer by an etching step, the wafer 14 is immersed in the treatment tub 11 with the main surface of the wafer being entirely covered by the resist. In addition, SiO.sub.2 can be deposited on a wafer by using the tub 11 as shown in FIG. 1, in which Al is dissolved in a saturated solution of H.sub.2 SiF.sub.6. When a liquid crystal display apparatus is manufactured, a larger chemical treatment tub 11 is used since larger wafers are used.
FIG. 2 is a crosssectional view showing an apparatus for plating a silicon wafer. A plating of a silicon wafer with Au bumps for use in TAB (Tape Automated Bump) process will be described with reference to FIG. 2. A plating solution tub 21 is filled with an Au plating solution 22 and heated to 60.degree. to 70.degree. C. A wafer 23 and an electrode 24 are placed opposite each other in the Au plating solution 22. A direct power source 25 supplies a current to plate the wafer 23. A power feeding portion 26 is provided at an end of the wafer 23.
Next, a deposition treatment on the silicon wafer will be described with reference to FIG. 3. To increase adhesion force between a positive photoresist and a wafer 33, a deposition treatment using a saline coupling agent such as HMDS (hexamethylenedisilane) is generally performed before the resist is applied to the wafer. In the deposition treatment, an HMDS liquid 32 and a wafer 33 are placed in a vessel 31 and then the vessel 31 is sealed hermetically. The HMDS liquid 32 is heated by a heating means 34 to be vaporized, vapor 35 of the HMDS liquid 32 forms an HMDS film on the wafer 33. In this way, the treatment of the wafer with coupling agent is completed.
FIG. 4 is a crosssectional view showing a treatment apparatus using a spray nozzle. First, a method of developing a positive photoresist will be described. A silicon wafer 41 is mounted on a rotary chuck 42 and fixed thereto. In a development treatment, the wafer 41 is rotated to be developed while a treatment liquid i.e., a developer, is being sprayed on the pattern-exposed resist on the wafer 41 by a spray nozzle 44. Otherwise, a developer may be dropped from the nozzle 44 and deposited on the wafer 41 by means of a surface tension, to develop the photoresist in a static state. Next, a method of applying photoresist will be described. In FIG. 4, a treatment liquid 43, i.e., photoresist, is dropped from the nozzle 44 instead of a developer and deposited on the wafer 41. Thereafter, the wafer 41 is rotated by the rotary chuck 42. As a result, superfluous photoresist is scattered and a photoresist layer of a desired thickness is applied to the wafer 41.
Regarding the treatments of the wafer 14 immersed in the chemical treatment tub 11, as shown in FIG. 1, the same treatment liquid 12 is always used several times since a great amount of the treatment liquid 12 is required. If the wafer 14 or the wafer holder 15 is contaminated, the contaminant is dissolved into the treatment liquid 12. Thus if the contaminated treatment liquid 12 is used to treat another wafer 14, then the wafer 14 is also contaminated. This is called cross-contamination. The treatment liquid 12 should be changed for every treatment to prevent this contamination. Hence this method is impractical because of its high cost. Moreover, even if the treatment liquid 12 is changed for every treatment, contaminant on the rear surface of the wafer 14 may be attached to the main surface of the wafer 14. Hence, it is impossible to prevent the cross-contamination. In addition, a serious accident may occur if the treatment tub 11 is damaged since a great amount of the treatment liquid 12 is used in the treatment tub 11. Thus, the method has a problem in safely.
In the plating of the wafer 23, as shown in FIG. 2, the rear surface of the silicon wafer 23 must be covered by the resist or the like, so that it is not plated. For this purpose, additional treatment steps are required. Moreover, the power feeding portion 26 is plated with Au since it is immersed in the plating solution 22 and therefore it is impossible to successively treat a number of wafers 23. In addition, since a great amount of the plating solution 22 must be used, a number of wafers 23 may be treated at a time to save cost. In such case the cross-contamination is unavoidable as in the case of the treatment shown in FIG. 1. Depending on the cause of the contamination, a quality of the plating cannot be duplicated.
In the deposition treatment shown in FIG. 3, the HMDS film is formed unnecessarily on the rear surface of the wafer 33. In the subsequent steps, dusts may be adhered to the HMDS film on the rear surface, resulting in occurrence of particles or contamination. Moreover, the HMDS may be deposited thickly on the inner wall of the closed vessel 31. Thus the thick HMDS film may peeled off to cause the particles. Moreover, when the whole space of the vessel 31 is filled with the HMDS vapor, it is difficult to make the HMDS concentration in the vessel 31 uniform. Therefore, the thicknesses of the HMDS films formed on the wafer 33 may be varied.
In the development treatment by the apparatus shown in FIG. 4, when the development is performed with the developer sprayed by the spray nozzle 44 on the rotating wafer 41, a radial nonuniformity in the developer is occurred. Further, in case the developer is dropped from the nozzle 44 on the stationary wafer 41, the nonuniformity in the developer occurs less. However, if the developer spreads slowly on the surface of the wafer 41, another nonuniformity in the developer may easily occur. For this reason, it is desirable that the developer be spread on the surface of the wafer 41 as quickly as possible. However, if the developer is spread too quickly, the surface tension of the developer is lost and then the developer cannot stay on the wafer 41. Thus the developer cannot be held on the surface of the wafer 41. Moreover, if the wafer is not placed horizontally, or vibrated or swayed due to wind, mechanical vibration, etc, the developer may also overflow the wafer 41. Moreover, when the diameter of the wafer 41 is as large as 200 mm or more, it is difficult to hold the developer on the wafer only by the surface tension.
In the photoresist applying treatment by the apparatus shown in FIG. 4, when the wafer 41 is rotated to scatter the superfluous resist, the solvent in the resist volatilizes. As a result, the viscosity of the resist increases. Thus, if the solvent volatility speed do not balance with the resist scattering speed, the resist film may undulate with the thickness thereof being greatly varied. This is called striation. To minimize the striation, a greater amount of the resist 43 is deposited on the wafer 41, or the rotation speed or acceleration of the wafer 41 is increased, for example. However, the striation cannot be overcome by these measures only as wafers 41 have become lager and larger.